1. Field of the Invention
The present invention relates to a production method for a base body for a liquid ejecting printing head (hereinafter simply referred to as xe2x80x9cprinting headxe2x80x9d), in which an electrothermal transducer and printing functional elements are formed on a substrate, and a production method for a printing head employing the base body for the printing head, and more particularly to a production method for a printing head employing the base body for a printing head to be employed in an ink-jet printing apparatus adapted to be used in a copy machine, facsimile, wordprocessor, or printer as an output device of a host computer, video output printer and so forth.
2. Description of the Related Art
Conventionally, the printing head is constructed by forming an electrothermal transducer element on a monocrystalline substrate, arranging a functional element for driving the electrothermal transducer element, a transistor array and so forth, outside of the silicon substrate, as a driver circuit for the electrothermal transducer element and connecting between the electrothermal transducer element and the transistor array by means of a flexible cable or wired bonding and so forth.
For the purpose of simplification of construction, reducing faulty product to be caused during production process and improvement for uniformity and reproductivity of characteristics of respective elements to be considered in head construction, there has been known an ink-jet printing apparatus having a printing head, in which the electrothermal transducer element and the functional element are formed on a common substrate, have been proposed in Japanese Patent Application Laid-open No. 72867/1982.
FIG. 1 is a section showing a part of the base body for the printing head constructed as set forth above. In FIG. 1, reference numeral 1801 denotes a semiconductor substrate of monocrystalline silicon. Reference numeral 1804 denotes an N-type semiconductor epitaxial region; and 1811 denotes an ohmic contact region of an N-type semiconductor with high impurity concentration. Reference numeral 1805 denotes a P-type semiconductor base region, and 1810 denotes an emitter region of a high impurity concentration N-type semiconductor. These regions form a bipolar transistor. Reference numeral 1816 denotes a silicon oxide layer as a heat accumulation layer and an interlayer insulation layer. Reference numeral 1817 denotes a heat generating resistor layer, 1818 denotes a wiring electrode of aluminum (Al), 1819 denotes a silicon oxide layer as a protective layer, 1812 denotes a base-collector common electrode of Al and 1820 denotes a Ta layer as a protective layer. These form the base body for the printing head including the electrothermal transducer. Here, reference numeral 1822 denotes a heat generating portion. The printing head is constructed as by forming an upper plate and a liquid passage on the base body constructed as set forth above.
On the other hand, while the construction set forth above is superior, there still exists room for improvement in satisfying high speed driving, energy saving, high package density, low cost, and high reliability which are strongly demanded for the recent printing apparatus.
At first, it is required to provide highly reliable printing head at low price. For achieving this, it becomes necessary to produce the printing head at satisfactorily high yield. Namely, conventional interlayer insulation layer 1816 and the protective layer 1819 and so forth are formed by depositing BPSG, SiO, SiO2, SiON, SiN and so forth at 300 to 450xc2x0 C. employing layer forming technology, such as normal pressure CVD, PE-CVD and so forth. However, in such temperature, wiring of Al or so forth or electrode or so forth causes a buno shaped bulge (often in the extent of 2 xcexcm in height and diameter) of Al or so forth called as hillock layer deposited (grown) by plasma CVD method and sputtering method, as shown in FIG. 2, for example, and grown. Then, by unevenness of the hillock 1101 and 1102, shorting is caused between wiring electrodes and between wiring and the protective layer of Ta (see protective layer 1820 shown in FIG. 1, for example) to result in operation failure to lower yield in production.
Therefore, it is a belief of the inventors that improvement of yield in production of the base body can be achieved by restricting growth of hillock in layer deposition by plasma CVD method and sputtering method.
Therefore, it is an object of the present invention to solve the above-mentioned technical problem and thus to provide a production method of a base body for a highly reliable printing head and the printing head at low cost and high yield. A protection method of a base body for a liquid ejecting printing head, according to the present invention, including an electrothermal transducer element for generating a thermal energy to be used in liquid ejection, a driving functional element driving the electrothermal transducer element, a plurality of wiring electrodes for connecting the driving functional element and the electrothermal transducer element, is characterized in that the protective layer is formed by depositing an insulative material over the electrothermal transducer element or the wiring electrode with elevating a temperature of the base body.
In such case, the base body temperature at a low temperature in the foregoing step is in a range of 200xc2x0 C. to 300xc2x0 C. and at a high temperature is in a range of 350xc2x0 C. to 400xc2x0 C. Further preferably, the base temperature at the low temperature is 300xc2x0 C. and the base body temperature at high temperature is 350xc2x0 C.
On the other hand, the protective later is selected among SiN, SiO, SiO2, SiON, PSG, BSG, BPSG, ZrO2, Al2O3, SiC, Si and Ta2O5. It should be noted that the materials of the protective layer formed at low temperature and the protective layer formed at high temperature are not necessarily the same. The protective layer formed at low temperature and the protective layer formed at high temperature are formed as two layer protective layer by switching the base body temperature. The two layer protective layer may be formed with various combinations of the insulative material listed above.
A production method of a liquid ejecting printing head having a base body for the liquid ejecting printing head, according to the present invention including electrothermal transducer element and a driving functional element for driving the electrothermal transducer element, is characterized by forming a P-type semiconductor layer by epitaxial growth on a P-type semiconductor substrate, and subsequently forming the driving functional element utilizing the P-type semiconductor.
A production method of a liquid ejecting printing head, according to the present invention, including a base body preparation process preparing a liquid ejecting printing head, in which an electrothermal transducer element, a driving functional element driving the electrothermal transducer element, a wiring electrode connecting the driving functional element and the electrothermal transducer element, a protective layer provided on the wiring electrode are formed on a substrate, and an ink ejecting portion forming step for forming ejecting portion having ejection opening for ejecting an ink, is characterized in that the production method of a base body for the liquid ejecting printing head includes a deposition step for forming the protective layer by depositing an insulative material on the wiring electrode with elevating a base body temperature in stepwise fashion or sequentially.
When the electrothermal transducer element has a heat generating resistor made of TaN, composition of TaN is to contain 1.9 to 1.0 of Ta relative to N in molecular weight ratio. The heat generating resistor may be made of HfB2, Poly-Si, Taxe2x80x94Al, Taxe2x80x94Ir, Au or Ag in place of TaN.
With the production method of the base body according to the present invention, the base body for the ink-jet printing head which is superior in durability, strong against repeatedly applied thermal impact, ink corrosion or cavitation, and can provide high quality printing images for a long period, can be efficiently produced.
Also, in the production method of the printing head according to the present invention, since the protective layer formed at low temperature is inserted, occurrence and growth of buno-shaped projections, called hillocks, during deposition (growth) of the layer by CVD method at high temperature, can be successfully prevented. Therefore, shorting between the wiring electrode or between the wiring and the protective layer of Ta due to unevenness due to hillocks 1101, 1102 as shown in FIG. 2, operation failure to cause lowering of production yield can be avoided. As a result, the printing head can be produced at high yield and thus highly reliable printing head can be provided at low price.
The above and other effects, features and advantages of the present invention will become more apparent from the following descriptions of the embodiments thereof taken in conjunction with the accompanying drawings.